This research links neuro- and cognitive psychology by asking whether performance of concurrent cognitive tasks can be facilitated by presentation of each task to a different hemisphere. Two major hypotheses will be tested by means of 3 experiments. I) Performance will be better when each task is presented to a different hemisphere if the two concurrent cognitive tasks require two different and contradictory kinds of processing (e.g. adding and subtracting). II) In contrast, performance will be better when both tasks are presented to the same hemisphere if the two concurrent cognitive tasks require the same kind of processing (e.g. only subtracting). Since each hemisphere receives information from the contralateral visual field, these hypotheses will be tested by comparing performance during Bilateral (i.e., two visual field; bihemispheric) presentation and Unilateral (i.e. single visual field; single hemisphere) presentation. Hypothesis I has been confirmed by preliminary research. The proposed research contains modifications which will enable us to eliminate some competing explanations for the phenomenon. In addition, the initial sample will be expanded by the inclusion of left handers (total number of subjects will = 128). If, as is predicted, the effect of dividing input between the two hemispheres differs in right and left handers, this will provide a first clue as to how "atypical" cerebral organization affects cognitive processing. Such a finding would lay the groundwork for investigation of other populations, such as those with unusual cerebral organization (e.g. dyslexics) or those with a restricted ability to divide attention between simultaneous streams of information (e.g. young grade school children). This research is also significant because of its relevance to several fundamental controversies. For example, why do we have a double hemisphere system instead of a single head ganglion? Is the sole function of the corpus callosum to "transfer" information between the hemispheres, or is it even more important for its role as insulator and inhibitor of cross-talk between the hemispheres? Is the recent discovery that the corpus callosum is larger in left handers than right handers related to the ability of left handers to simultaneously perform contradictory operations in the two hemipsheres? The proposed experiments represent the first leg of a program which would address these issues.